The oxo process is the commercial application of the hydroformylation reaction for making higher alcohols and aldehydes from olefins. In the cobalt oxo process, an olefin reacts with carbon monoxide and hydrogen (i.e., syn gas) at elevated temperatures in the presence of a cobalt carbonyl catalyst to produce a hydroformylation reaction product which is subsequently decobalted or demetalled to produce a crude product mixture of aldehydes, alcohols, acetals, formates, unreacted olefins and secondary products. Subsequent hydrogenation steps provide the desired finished alcohol products commonly referred to as oxo alcohols (i.e., alcohols produced by an oxonation reaction).
One aspect of the overall cobalt oxo process involves the preparation of the active cobalt catalyst species which is hydrido cobalt tetracarbonyl (HCo(CO).sub.4). Commercial oxo processes employ a preforming step in which this active cobalt catalyst species is prepared using a noble metal preforming catalyst which is contacted with a cobalt salt, e.g., cobalt formate, to provide the desired HCo(CO).sub.4 species.
This preforming step is disclosed, for example, in U.S. Pat. No. 4,404,119, which issued Sep. 13, 1983, to Lagace et al. and in U.S. Pat. No. 4,255,279, which issued Mar. 10, 1981, to Spohn et al., and U.S. Pat. No. 5,237,105, which issued Aug. 17, 1993, to Summedin, all of which are incorporated herein by reference.
Particularly preferred preformer catalysts are set forth in co-pending U.S. patent application, Ser. No. 08/217,298 (Hill, Jr. et al.), which was filed on Mar. 22, 1994, now U.S. Pat. No. 5,434,318. These conventional preformer catalysts comprise Group IB and VIII metals such as palladium, platinum or gold. Such catalysts may be supported or unsupported using supports such as silica, alumina, zeolites or activated carbon and other carbonaceous support material. One particularly desirable preformer catalyst is 2 wt. % palladium supported on activated carbon.
The present inventor has discovered that the use of a shell-type, metal on substrate, catalyst wherein the metal is placed on the exterior surface of the substrate as opposed to being uniformly impregnated throughout the entire substrate as are the catalyst disclosed in co-pending U.S. patent application, Ser. No. 08/217,298 (Hill, Jr. et al.), allows for improved conversion of the cobaltous salt to hydrido cobalt tetracarbonyl in the preformer reactor.
The increased process efficiency obtained by utilizing the shell-type, metal on substrate, catalyst translates into increased processing capacity for a given commercial scale reactor. Reactor vessels can be reduced in size in direct proportion to the rate constant improvement allowing significant reduction in initial capital investment for the preformer reactor.
Still another advantage of the present invention is reduced catalyst cost while maintaining processing capacity. That is, a smaller amount of the shell-type catalyst of the present invention is required to convert a cobalt salt to the desired HCo(CO).sub.4 compared to the amount required by conventional preformer catalysts to attain similar conversion levels.
The present invention also provides many additional advantages which shall become apparent as described below.